This study will explore the differential responses by age to the economic incentives implicit in the Workers' Compensation insurance program, the nation's social insurance scheme for industrial injury and disease. Parametric and Nonparametric maximum Likelihood methods will be applied to test whether the distribution of the durations of nonwork spells arising from occupational injury or disease vary over age groups, and if so, why they vary. Specific economic hypotheses to be tested include: Durations vary inversely with wages, and Durations vary directly with social insurance (Workers' Compensation) benefits. The research method employed in the study allows for both nonparametric heterogeneity controls and explicit test of the underlying structural distribution. This technique enables one to utilize the advance introduced into the literature by Professors Hechman and Singer (nonparametric controls to enable retrieval of consistent point estimates of underlying structure) and parametric tests of the appropriateness of that structure.